Imitation by infants and their mothers has been proposed as a significant contributor to children's language and cognitive development. Rates of spontaneous vocal, verbal, and action imitation by normal infants and their mothers vary widely, and greater imitation, especially verbal imitation, by both partners is associated with children's faster development, including language development. For this reason, several intervention programs for children with disabilities have encouraged them or their mothers to imitate. Because information on imitation by normal infants and mothers is prerequisite to developing the most effective interventions for children with disabilities, the long-term goals of the research are to identify the causes of normal infants' and mothers' individual differences in imitation and the means by which these differences predict development of language and cognition. This project will investigate mothers' and infants' responses to being imitated by their partners. It will examine mothers' and infants' responses to their partners' spontaneous vocal, verbal, and action imitation during naturally occurring dyadic interactions during free play and bath sessions in the participants' homes. Developmental changes and individual differences will be analyzed in an existing longitudinal sample observed at 10, 13, 17, and 21 months. The kinds of responses mothers provide to their infants' imitation may account for individual differences in infants' imitative rates. Infants' behaviors in response to imitation by their mothers, in turn, may elucidate the mechanism by which maternal imitation predicts children's verbal development. Infants' responses to being imitated also merit examination as potential indicators of their recognition of being imitated, a process proposed as a precursor to children's development of a theory of mind. [unreadable] [unreadable] [unreadable]